1. Field of the Invention
The present invention relates to a liquid crystal display panel used in a display device for OA (Office Automation) and the like and particularly, to a liquid crystal display panel with high luminance.
2. Description of the Related Art
A liquid crystal display panel of an active matrix type is the main stream of liquid crystal display panel. In an active matrix liquid crystal display panel, a liquid crystal is contained between two transparent substrates which are disposed in parallel to each other and display is controlled by applying voltage to the liquid crystal in a direction perpendicular to the transparent substrates. In a liquid crystal display panel of this voltage application type, however, there arises a drawback that a contrast of display is strongly affected according to a viewing angle.
Therefore, in recent years, a liquid crystal display panel of an IPS type, in which a change in contrast according to a viewing angle is diminished and wide viewing angle characteristics can be achieved by applying voltage to transparent substrates in parallel thereto, has been developing toward commercialization.
In a liquid crystal display panel of the IPS type, however, display is affected by electric fields occurring due to a potential change of a signal line after writing to a pixel and a potential change of an adjacent signal line.
Therefore, in order to prevent such an influence on display from occurring, there has been disclosed a liquid crystal display panel in which a common electrode line having a width equal to or more than a predetermined value is interposed between a signal line and a pixel adjacent to each other (see Japanese Patent Application Laid-Open No. Hei 9-15650). FIG. 1 is a schematic view showing a conventional liquid crystal display panel.
In the conventional liquid crystal display panel of the IPS type, a plurality of signal lines 54 and a plurality of scanning lines 55 intersected with each other are provided. A region which is surrounded by adjacent signal lines 54 and adjacent scanning lines 55 is a display section 57 of a fundamental pixel unit. Further, a pixel electrode 52 extending in the same direction as that of a signal line 54 is disposed in a central portion of the display section 57. A thin film field effect transistor 51 whose gate is connected to the scanning line 55 is provided. The drain of the thin film transistor 51 is connected to the signal line 54 and the source thereof is connected to a pixel electrode 52.
In addition, a common electrode line 56 extending in the same direction as that of the scanning line 55 is provided between the pixel electrode 52 and the scanning line 55 to which the thin film transistor 51 of the fundamental pixel unit is not provided. Further, opposite electrodes 53 extending in the same direction as that of the signal line 54 are provided between the pixel electrode 52 and both of the two signal lines 54 in the fundamental pixel unit. The opposite electrodes 53 are connected to the common electrode line 56.
In the mean time, these elements such as the thin film transistor 51 described above are disposed on one of the two transparent substrates.
With the conventional liquid crystal display panel thus constructed, a cross talk is alleviated, and a good image quality and a wide viewing angle are achievable.
However, since the common electrode 56 is provided on such a conventional liquid crystal display panel as described above, an effective region (opening section) where display is actually effected is narrow compared with a twisted nematic (TN) type. Therefore, the conventional liquid crystal display panel has a problem that high luminance is hard to be realized.
Accordingly, it is an object of the present invention to provide a liquid crystal display panel by which high luminance is achievable while securing a wide viewing angle.
According to one aspect of the present invention, a liquid crystal display panel may comprise a transparent substrate, a thin film transistor provided on the transparent substrate, and a pixel electrode provided on the transparent substrate. A scanning line connected to a gate of the thin film transistor may be provided on the transparent substrate. A voltage which controls the thin film transistor may be applied to the scanning line from an external circuit. An opposite electrode connected to a source of the thin film transistor may be provided on the transparent substrate. A potential difference between the opposite electrode and the pixel electrode may be a voltage applied to a liquid crystal. A common electrode line connected to a drain of the thin film transistor may be provided on the transparent substrate. A voltage which controls a potential of the opposite electrode is applied to the common electrode line from the external circuit.
According to one aspect of the present invention, when the thin film transistor is made to assume the OFF state by a voltage applied to the scanning line, the opposite electrode assumes an electrically open state. Therefore, a voltage between a pixel electrode and the opposite electrode is held constant until the thin film transistor assumes the ON state in the next stage even if the potential of the pixel electrode changes. Hence, wiring that has conventionally been used to eliminate influence of electric field is unnecessary, which enables an opening section to be widely secured. Thereby, high luminance can be assured.
The pixel electrode and the opposite electrode preferably have regions respectively which are superimposed on each other in a thickness direction of the transparent substrate.
Further, the common electrode line is shared by adjacent pixels and interposed between the adjacent pixels.
Besides, the liquid crystal display panel may include a signal line connected to the pixel electrode. The opposite electrode may be surrounded by the common electrode line, the pixel electrode and the signal line.
In addition, the common electrode line and the scanning line may be substantially arranged in parallel to each other. The common electrode line and the signal line may substantially perpendicularly intersect with each other.
According to the present invention, since an influence which electric field exerts on a display can be eliminated even if there is provided no wiring which has been understood to be necessary in the prior art, the wiring is unnecessary. Hence, a wide opening section can be secured, thereby enabling high luminance to be achieved while securing a wide viewing angle.